In 1994, a technical working group under the auspices of the T-15 Technical Committee on Substructures and Walls of the American Association of State Highway and Transportation Officials (AASHTO) Bridge Subcommittee, was formed to reevaluate the design specifications for mechanically stabilized earth (MSE) walls contained in the AASHTO Standard Specifications for Highway Bridges (1996). One of the areas of focus was the internal stability design of MSE walls. Several methods for calculating the backfill reinforcement loads were available at that time in the AASHTO Standard Specifications, and the intent was to unify the design methods to simplify and clarify the specifications. To accomplish this, full-scale MSE wall case history data were gathered and analyzed so that the unified method developed could be calibrated to the empirical data, since all of the methods available were empirical in nature. The effect of simplifications in the method, such as how vertical soil stresses are calculated and how reinforcement stiffness is considered in the design, could also be evaluated with these full-scale wall data to ensure that the unified method developed was adequately accurate. From this effort, the AASHTO Simplified Method was developed.
This report summarizes the development of the Simplified Method. It uses a number of full-scale MSE wall case histories to compare the prediction accuracy of the Simplified Method to that of the other methods currently available and focuses primarily on steel reinforced MSE walls. The theoretical assumptions used by the Simplified Method, as well as the other methods, are also evaluated and compared in light of the empirical evidence. This evaluation showed that the prediction accuracy of the Simplified Method is at least as good as that of the other methods, while the Simplified Method still simplifies calculations. This evaluation also showed, however, that all of the methods have limitations that must be considered.